This invention relates to electromagnetic coils or solenoids and, more particularly, it concerns a bobbin structure which may be machine-wound to provide a solenoid with coupling terminals for releasable mechanical connection to an electric circuit.
Machine-wound solenoids typically include a bobbin having a hollow cylindrical mandrel extending between a pair of annular flanges, and a pair of electrical terminal posts located in the plane of one of the flanges. The bobbin is wound with wire to form an electrical coil from which the wire extends as leads to be wrapped around each of the terminals. Machine wrapping of one or both of the wire leads on the electrical terminal posts has, in general, required that the terminal posts be located in the plane of one of the flanges so that tension may be maintained in the wire as the lead is wrapped around the terminal. Otherwise, the final revolutions of wire on the coil will be loose and may become tangled or unravelled. Also, the terminal posts are generally formed of relatively heavy or bar-like conductive metal to lend rigidity and strength adequate to withstand the forces imposed by winding the wire leads under tension as well as to facilitate a soldered connection of power circuit leads to the post and thus to the coil.
In many applications of small machine-wound solenoids, such as for actuation of electronic shutters in photographic cameras, constraints imposed by such factors as the size and configuration of space available to receive the solenoid, facility for cost-effective assembly procedures and the like, present problems to the use of machine-wound solenoids of the type aforementioned. For example, the terminal posts, in projecting beyond the periphery of the coil, represent an added space requirement both in themselves and in the accommodation of power circuit lead connections to the posts. With respect to assembly procedures, it is often desirable from the standpoint of cost effectiveness to assemble the solenoid with the mechanical components to be operated thereby prior to completing the electrical connection of circuit leads with the terminal posts. The subsequent connection of power circuit leads to the preassembled solenoid, however, is most effectively and reliably accomplished by a plug-in type connector which is not readily accommodated by the design configuration of conventional machine-wound solenoids.